Benjamin Wedro, MD, FACEP, FAAEM

Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

Heat exhaustion definition and facts

Heat exhaustion is one part of the spectrum of heat-related illnesses that begin with heat cramps, progresses to heat exhaustion, and finally to heat stroke.

The body cools itself by sweating and allowing that sweat to evaporate. This requires enough fluid in the body to make sweat, air circulating across the skin, and low enough air humidity to allow that sweat to evaporate.

Causes of heat exhaustion include activity in a hot environment that can overwhelm the body's ability to cool itself, causing heat-related symptoms, and living in a hot environment without adequate access to water for dehydration.

Heat exhaustion can progress to heat stroke when the body's temperature regulation fails. The person develops a change in mental status, becomes confused, lethargic, and may have a seizure, the skin stops sweating, and the body temperature may exceed 106 F (41 C). This is a life-threatening condition and emergency medical attention is needed immediately.

First aid treatment for heat exhaustion includes recognizing the symptoms, stopping the activity, and moving to a cooler environment. Rehydration with water or a sports drink is the cornerstone of treatment for heat exhaustion.

Complications of heat exhaustion include nausea, vomiting, dehydration and muscle weakness. If the activity is not stopped and the person left in a hot environment, there can be progression of symptoms to heat stroke, a life-threatening emergency.

Heat exhaustion can be prevented by being aware of your environment, especially on hot, humid days, and drink lots of fluids (no alcohol or caffeine).

Infants, children, and the elderly are at risk because their bodies are less able to get rid of (dissipate) heat.

Infants and children are particularly at risk during hot weather. Never leave an infant, toddler, or child in the car when it is hot. An average of 38 children die each year after being trapped inside motor vehicles. When outside temperatures reach 80 F to 100 F (27 C to 38 C) the internal temperatures of vehicles parked in direct sunlight can reach up to 131 F to 172 F (55 C to 78 C). The inside of a vehicle with the windows rolled down two inches can reach 109 F (42.7 C) within 15 minutes.

Dogs and other pets also are at risk for heat exhaustion and heat stroke. They do not sweat through their skin and fur, but instead cool themselves by their footpads, and panting and through their noses and mouths. Pet owners need to be aware of the environment and prevent prolonged exposure to heat, and provide adequate water to prevent dehydration. Never leave your pet in a vehicle when it is hot.

What is heat exhaustion?

The body cools itself most efficiently by sweating and having that sweat evaporate. Should sweating be unable to meet the cooling demands of the body, heat-related illness can occur. This is a spectrum of conditions with minor symptoms such as prickly heat or heat rash, progressing to heat cramps, then heat exhaustion, and finally to heat stroke, a life-threatening medical condition.

The line between each diagnosis is not sharply drawn. Heat cramps describe involuntary spasm of the large muscles of the body, while heat exhaustion has more systemic complaints such as the signs and symptoms listed above.

The affected individual may be a low-grade fever. Heat stroke is a life-threatening situation where the body's cooling system fails. The body temperature spirals out of control usually greater than 106F (41 C), sweating stops, and there are mental status changes like confusion, seizure, or coma.

Heat exhaustion occurs when a person exercises or works in a hot environment and sweating cannot dissipate the heat generated within the body. Often dehydration occurs because the person hasn't replaced the water lost by sweating. Heat exhaustion also may occur if a person lives in a hot environment without adequate air circulation and does not drink an adequate amount of water.

What is the difference between heat exhaustion and heat stroke?

There is no set line that distinguishes heat exhaustion from heat stroke. If a person is suffering from a heat-related illness such as heat exhaustion, and changes in mental status occur, he or she should be considered to be suffering from heat stroke. This includes confusion, lethargy, seizure, or coma. This is a medical emergency, and if treatment is delayed mortality can be greater than 50%. While victims of heat exhaustion sweat profusely, people suffering from heat stroke stop sweating and have dry skin. This is a warning sign of impending heat stroke.

What are the signs and symptoms of heat exhaustion?

As dehydration increases from the loss of body water, lightheadedness may occur and fainting (syncope) may occur, especially if the affected individual stands up quickly (due to orthostatic hypotension).The person also may have a low-grade fever.

What causes heat exhaustion?

Heat exhaustion occurs when a person exercises and works in a hot environment and the body cannot cool itself adequately. Dehydration occurs with water loss from excessive sweating, which causes muscle cramps, weakness, and nausea and vomiting. The nausea and vomiting makes it difficult to drink enough fluid to replenish the body's water supply, and the lack of body water impairs further sweating, evaporation and cooling.

Relative humidity is an important factor in developing heat exhaustion. If the humidity is too high, sweat on the skin cannot evaporate into the surrounding air and body temperature cooling fails.

Living in a hot environment may predispose a person to heat exhaustion. During a heat wave, the elderly, the poor, and those who live an isolated life may not have access to air conditioning and are at risk of heat-related illnesses.

Who is at risk for heat exhaustion?

Heat exhaustion usually affects people who are working or exercising in a hot environment, and those who do not have access to adequate water. Those at risk for heat exhaustion include:

Infants and young children are at risk because their temperature regulation mechanisms are not fully developed. They also are dependent upon others for water and appropriate clothing.

The elderly are similarly at risk because of underlying medical conditions that limit the ability to sweat including poor circulation, skin changes, and chronic medication usage.

Socioeconomic issues increase the risk of heat exhaustion if access to air conditioning is limited. During heat waves, large cities often open cooling centers to help minimize the risk of large numbers of people succumbing to heat-related illness.

Certain medications such as antidepressants, antipsychotics, and tranquilizers may impair the ability of the body to sweat.

The body has the ability to acclimate to hot weather but if heat waves come suddenly, or if a person travels from a cooler environment to a hot environment, the risk of heat exhaustion increases. It takes about 7 to 10 days for the body to adapt to hot weather. A non-acclimated person can produce a liter or almost a quart of sweat in an hour to assist in cooling the body. A person who is acclimated to the heat can produce 2 or 3 liters of sweat per hour, doubling or tripling the cooling potential for the body.

This water lost in sweat needs to be replaced for the sweating/cooling mechanism to work. A liter of sweat weighs 1 kilogram or 2.2 pounds.

When should an individual seek medical care for heat exhaustion?

Heat exhaustion usually can be treated at home as long as the affected individual can replace the lost fluid, keep well hydrated, and find a cool place to rest. Water, electrolyte replacement solutions, or sport drinks are appropriate to consume. If nausea and vomiting prevent rehydration, the individual should seek medical attention, and may need IV fluids for rehydration.

Muscles cramps can be severe and if stretching and rehydration cannot relieve recurrent cramps, medical care may be necessary.

It is important to recognize that if the person stops sweating, becomes confused, or has a seizure, heat stroke, a life-threatening condition, may be developing. Emergency medical services should be activated immediately (call 911 if available). The affected individual should be moved to a cooler place, have their clothing removed, and attempts should be made to cool the body with cold compresses, spraying or sponging the body with cool water and promoting air circulation with oscillating fans.

Laboratory tests are not routinely performed unless the health care professional is concerned about electrolyte imbalance or significant dehydration and kidney failure.

However, it is important for the health care professional to consider other diagnoses, since there are many infectious illnesses that accompany a fever, weakness, nausea and vomiting. This is especially the case in the elderly and very young. In these groups, heat exhaustion may be a diagnosis of exclusion, meaning that other more serious illnesses should be considered before settling on heat as the cause of the problem. History and physical examination may be all that is needed.

What is the first aid treatment for heat exhaustion?

Cooling and rehydration are the cornerstones for treating heat exhaustion. The affected individual should stop their activity, and then move or be moved from the hot environment to a cooler environment. The person may be placed in the shade or taken to an air-conditioned environment (don't forget that cars have air conditioning). Clothes may be removed to help with air circulation across the body. Misting the skin with cool water also helps by stimulating evaporation and cooling the body.

Rehydration is the next important step in treating heat exhaustion. This may be a challenge if the person begins to suffer from nausea and vomiting. Small sips of water, a mouthful at a time, might be tolerated even if some vomiting persists. Water, sports drink and other electrolyte replacement drinks are reasonable options.

If oral rehydration fails or if symptoms persist, intravenous fluids may be required to replace the water loss because of the excessive sweating. Hydration continues until the patient begins to urinate, a signal that the kidneys have sensed that there is enough fluid in the body, and it no longer retains fluid.

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What are the complications of heat exhaustion?

Heat exhaustion is one part of the spectrum of heat-related illness, and symptoms should be reversible with treatment. However, some affected individuals do not recognize their symptoms and if they are not removed from the hot environment, cooled, and rehydrated, the heat-related illness can progress to heat stroke, a life-threatening condition.

Individuals who have suffered from heat exhaustion are more prone to experience another episode and should be cautious when working or exercising in hot conditions.

How can heat exhaustion be prevented?

Understanding one's environment is perhaps the most important step in preventing heat-related illness. If possible, strenuous activities should not be performed in excessively hot or humid environments. However, people often have to work in the heat of the day, or indoors in hot situations and need to make the effort to protect their bodies. These can include frequent breaks taken in a cooler areas, adequate fluid intake, and slowing the pace of work to decrease heat generated by the body.

A person at risk for heat exhaustion should watch their urine output to monitor their hydration status .If the body is dehydrated, the kidneys will hold onto water, and make concentrated, strong smelling urine. If enough water is present, the urine will turn clear.

Acclimating to conditions allows the body to perform in situations that would otherwise be difficult. The body will make physiologic changes allowing it to cool more efficiently, if it has gradual exposure to hot conditions. Moving from a cool to very hot environment quickly increases the risk of developing heat related-illness symptoms.

It is important to look after family and loved ones during heat waves. When the temperature rises, the elderly or those less fortunate may not have air conditioning or the ability to cool their homes. Cities often set up cooling centers when the heat index rises, and there is an increased risk of heat-related illness. In 1995, Chicago experienced a record heat wave that killed hundreds of people. Most were elderly and the poor who had no air conditioning or could not afford to use it. Some wouldn't open their windows for fear of crime. In 2015, heat waves were responsible for more than 5,000 deaths in India and Pakistan.

What is the prognosis for heat exhaustion?

Most individuals recover well from heat exhaustion. The key to recovery is recognizing symptoms before they progress to heat stroke. The earlier the activity is stopped, the individual is cooled and hydration begins, the greater the likelihood that complications will not occur.